As a general rule, mobile radio systems are covered by standards, and the corresponding standards published by the corresponding standards bodies may be referred to for more information.
FIG. 1 outlines the general architecture of a mobile radio system, which essentially comprises:                a radio access network (RAN) 1, and        a core network (CN) 4.        
The RAN comprises network elements such as base stations 2 and base station controllers 3. The RAN communicates with mobile terminals 5 via an interface 6 and with the CN 4 via an interface 7. The CN 4 communicates with external networks (not specifically shown). Inside the RAN, the base stations 2 communicate with the base station controllers 3 via an interface 8.
In the UMTS, which is a third generation system, the RAN is called the UMTS Terrestrial Radio Access Network (UTRAN), a base station is called a Node B, a base station controller is called a Radio Network Controller (RNC) and a mobile terminal is called a User Equipment (UE). The interface 6 is called the Uu interface, the interface 7 is called the Iu interface and the interface 8 is called the Iub interface; there is also an interface 9 between RNCs, called the Iur interface. The CN contains in particular Mobile Switching Center (MSC) network elements 10 used for circuit mode connections and Serving General Packet Radio Service (GPRS) Node (SGSN) network elements 11 used for packet mode connections. The RNC/MSC interface is also called the Iu-CS interface, where CS stands for “circuit-switched”, and the RNC/SGSN interface is also called the Iu-PS interface, where PS stands for “packet-switched”. The interface Uu is also called the radio interface and the Iub, Iur, and Iu (Iu-CS, Iu-PS) interfaces are also called terrestrial interfaces.
The RNC controlling a given Node B is called the Controlling Radio Network Controller (CRNC). The CRNC has a load control and radio resource allocation role for each Node B that it controls and the cells covered by those Nodes B. For a given call relating to a given UE, there is a Serving Radio Network Controller (SRNC) having a control role in relation to the call concerned. A Node B connected to the UE but not controlled by the SRNC communicates with the SRNC via the RNC controlling it, which is also known as the Drift RNC (DRNC), and via the Iur interface.
The network elements of the RAN are interconnected by a transport network, not specifically shown in FIG. 1. A logical link within the transport network enables two network elements to communicate via one of the terrestrial interfaces Iub, Iur, and Iu (Iu-CS, Iu-PS).
As a general rule, systems of the above kind must be able to support traffic whose Quality of Service (QoS) requirements can differ greatly from one traffic to another. The QoS architecture in a system such as the UMTS is defined in particular in the Technical Specification TS 23.107 published by the 3rd Generation Partnership Project (3GPP). This QoS architecture is based on support services characterized by QoS attributes. Different support services are distinguished, such as in particular Radio Access Bearer (RAB) services, Radio Bearer (RB) services, and Iu bearer services. Different QoS attributes are distinguished, such as in particular the traffic class, the maximum bit rate, the guaranteed bit rate, the transfer delay, the traffic handling priority, etc. Four traffic classes are further distinguished, respectively for conversational, streaming, interactive, and background applications. It is also possible to distinguish circuit mode services or real-time services (such as voice services in particular), for which the traffic class is generally the conversational class, which is the most demanding in terms of transfer delay, and packet mode services, or non-real time services (such as in particular web browsing services, electronic mail (e-mail) services, etc.), for which the traffic class is generally a class other than the conversational class, and less demanding in terms of transfer delay.
As a general rule, a model has been defined for the communications protocols at the terrestrial interfaces which makes a distinction between a radio network layer corresponding to functions relating to radio access, independently of the technology used for transport at the terrestrial interfaces, and a transport network layer corresponding to functions associated with transport, and depending on the technology used for transport at the terrestrial interfaces. Furthermore, a user plane and a control plane are distinguished for each of these layers, the two planes corresponding to two types of data that can be communicated in accordance with the above protocols, namely data corresponding to traffic sent or received by a UE (user data) and data corresponding to signaling (or control data) necessary to the operation of the system. Two types of signaling can also be distinguished, namely signaling associated with the radio network layer and signaling associated with the transport network layer.
The signaling relating to the radio network layer corresponds in particular to the following protocols, which are also known as application protocols:                for the Iu interface, the Radio Network Application Part (RANAP) protocol, defined in particular in Technical Specification TS 25.413 published by the 3GPP,        for the Iub interface, the Node B Application Part (NBAP) protocol, defined in particular in Technical Specification TS 25.433 published by the 3GPP, and        for the Iur interface, the Radio Network Subsystem Application Part (RNSAP) protocol, defined in particular in Technical Specification TS 25.423 published by the 3GPP.        
The RANAP protocol covers in particular signaling relating to Radio Access Bearer (RAB) set-up. The NBAP protocol covers in particular signaling relating to radio link set-up for cells controlled by the SRNC. The RNSAP protocol covers in particular signaling relating to radio link set-up for cells controlled by the DRNC.
As a general rule, transport at the terrestrial interface level is in packet mode. Remember that in circuit mode the transmission resources are assigned in a fixed manner to different users, whereas in packet mode the transmission resources are shared at any given time by different users, which makes it possible to optimize the use of available transmission resources. However, packet mode implies the possibility of congestion and packet loss. Techniques such as connection admission control in particular are generally used to prevent congestion and thereby to guarantee the QoS within the transport network.
One transport technology used in the UTRAN is the Asynchronous Transfer Mode (ATM) technology based on asynchronous time-division multiplexing of small packets of fixed size known as cells. As a general rule, the ATM technology is covered by standards and the corresponding standards published by the corresponding standards bodies may be referred to for more information. Remember simply that an ATM network can be modeled by means of an ATM layer and an ATM Adaptation Layer (AAL) between the ATM layer and users. The ATM layer is connection-oriented and transmits cells between a source and a destination over a logical connection that is also referred to as a Virtual Channel (VC). A plurality of virtual channels can be grouped together to form a Virtual Path (VP). To apply the ATM technology to transport within the UTRAN, a dedicated AAL layer, called the AAL2 layer, is used for user data. When a UE communicates with the UTRAN, a corresponding AAL2 logical connection is set up at one or more of the terrestrial interfaces concerned of the UTRAN.
In the case of the ATM technology, the signaling relating to the transport network layer includes the Access Link Control Application Part (ALCAP) protocol as defined in particular in specifications Q.2360-1 and Q.2360-2 published by the International Telecommunications Union (ITU-T).
Technologies other than the ATM technology can be used in the transport network, such as in particular the Internet Protocol (IP) technology. As a general rule, the IP technology is also covered by standards, and the corresponding standards published by the corresponding standards bodies may be referred to for more information.
As a general rule, it is very important to dimension these networks correctly, in particular the RAN, to optimize quality of service for users and costs for the operator. If a network is overdimensioned, the QoS is generally guaranteed for users, but this is not generally economic for the operator, since transmission resources are then provided or reserved that may not be used. Conversely, if a network is underdimensioned, this is generally more economic for the operator but less acceptable for users, since the QoS may not be guaranteed.
In the same way as a distinction is drawn between the radio network and the transport network, it is possible to draw a distinction between the dimensioning of the radio network and the dimensioning of the transport network.
The particular problem for dimensioning the radio network is that of determining the density of cells, their capacity or configuration (including for a Node B, for example, its processing capacity or hardware configuration, the number of bearers assigned, etc.), and parameters that can be configured by the operator (such as handover, power, admission, and load control parameters, for example), etc. More generally, the problem is that of determining any element or parameter for dimensioning the radio network, in particular in terms of capacity, coverage, and quality of service.
The particular problem in dimensioning the transport network is that of determining the capacity or configuration of the logical links corresponding to the Iub, Iur, and Iu (Iu-CS, Iu-PS) interfaces. More generally, the problem is that of determining any element or parameter for dimensioning the transport network, in particular in terms of capacity and quality of service.
Initial dimensioning, prior to commissioning, is generally effected during a preliminary planning phase. Dimensioning can be optimized after commissioning. To this end, network observations or measurements can be effected on the network when in operation and the dimensions of the network modified or adapted accordingly.
These dimensioning problems have been the subject of a great deal of research, examples of which may be found in the literature. However, this research generally relates dimensioning the radio network, and not to dimensioning the transport network. Moreover, these dimensioning problems are generally more complex to solve for third generation systems than for second generation systems. In particular, the Universal Mobile Telecommunications System (UMTS), which is a third generation system, uses a Code Division Multiple Access (CDMA) radio access technology, whereas the Global System for Mobile communications (GSM), which is a second generation system, uses a Time Division Multiple Access/Frequency Division Multiple Access (TDMA/FDMA) radio access technology. Furthermore, second generation systems use transport technologies based on circuit mode whereas third generation systems use transport technologies based on packet mode.